1. Field of Invention
The present invention relates to couplings to facilitate clean breakaway of road-side signs of the type carried on posts if the posts are struck by an automobile.
2. Description of Prior Art
Stop signs, as well as many other road side signs, are conventionally installed with a ground stake (or anchor), a square sign post, the sign, a set of angled fasteners, and a set of straight fasteners. The ground stake is hollow steel tube construction, with an approximately square (i.e., square or rectangular, hereinafter referred inclusively as square) cross-section profile, and is installed into the ground in a vertical position with approximately zero to four inches of the stake extending above the ground. The sign post is also hollow steel tube construction, with an approximately square cross-section profile. The bottom of the sign post is snugly slipped into the top of the ground stake, and is secured in the ground stake with the angled fasteners extending through aligned clearance holes in the top of the post and the bottom of the ground stake. The sign is secured to the top of the post with the straight fasteners. Details of a conventionally installed stop sign are discussed further below and shown in the drawings in FIGS. 1-3.
The currently used telescoping posts were approved by the FHWA in 1986. However, they are not a breakaway system in that at speeds over 30 mph the signpost when struck by a vehicle will come back on the vehicle and will likely penetrate the windshield or roof causing possible occupant injury. At slow speeds the signpost may fall forward but become lodged in the ground anchor making it difficult to remove. In both cases the anchor becomes disfigured and will need to be replaced.
More particularly, experience shows that such conventionally installed road side signs present the potential for damage to an automobile that strikes the post, and the potential for injury to occupants of the automobile. As illustrated in FIG. 4 of the drawings, when an automobile strikes a conventionally installed stop sign post, particularly when struck at speeds of greater than approximately 30 miles per hour, there is a potential that the sign post will bend back towards the automobile, sending the sign towards the automobile and its occupants. Numerous accidents are recorded each year in which stop signs slam back into the roof of a car that strikes the sign post head-on, potentially piercing through the roof, and/or back through the windshield. These scenarios present a genuine danger of injury to the occupants of the vehicle.
Prior sign post breakaway coupling arrangements tend to be relatively complicated and correspondingly expensive. Some prior sign post breakaway couplings require modification to the ends of the conventional ground stake and/or the conventional sign post noted above, and/or require rivets or special fasteners and/or special tools for installation of the coupling to the post and the ground stake, and for removal of the post and coupling from the ground stake.
The National Cooperative Highway Research Program (NCHRP) Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features, specifies the generally accepted breakaway performance criteria of breakaway couplings for road signs.
There is a need for a new breakaway coupling for installing road-side signs that reduces the dangers associated with striking a conventionally installed stop sign, and that is relatively simple in construction and installation, and correspondingly less expensive as compared with prior breakaway couplings. There would also be cost and safety advantages if such a technique or device could be used with both newly installed stop signs and retrofit to currently installed signs without the need to modify either the ground stake or the sign post.